Magnetic head having a wear-resistant layer, and method of manufacturing such a magnetic head

ABSTRACT

Magnetic head having a head face ( 5 ) and comprising a head structure composed of thin layers and provided with a transducing element (E 11 ), in which different materials occurring in different areas are present in the head face. The head face is provided with a first layer ( 31 ) of a material which is more sensitive to corrosion than said materials in the head face, and the first layer is provided with a second layer ( 33 ) of a wear-resistant material which is more insensitive to corrosion than the material of the first layer. The second layer constitutes a contact face ( 35 ) for cooperation with a magnetic tape ( 7 ).

[0001] The invention relates to a magnetic head having a head face andcomprising a head structure composed of thin layers and provided with atransducing element, in which different materials in different areas arepresent in the head face.

[0002] A magnetic head of this type is known from JP-A 63-37811(herewith incorporated by reference). The known magnetic head has athin-film structure provided on a substrate and comprises a magneticyoke with a magnetoresistive element and a transducing gap. The magnetichead also has a head face in which the transducing gap and magnetic fluxguides for guiding magnetic information towards the magnetoresistiveelement terminate. The head face of the known magnetic head is used forguiding a magnetic record carrier, particularly a magnetic tape.

[0003] In magnetic heads which have a layer structure, soft materials,notably soft-magnetic materials of flux guides, for example permalloy,occur in addition to relatively hard materials, notably substratematerials, for example Al₂O₃/TiC. Due to the abrasive effect of therecord carrier moving along the head face during operation, therelatively soft materials may wear on the head face, which results in ahollowing of the layer structure of the head face. Such a hollowingleads to a larger distance between the record carrier and the layerstructure and hence to a reduced transfer of information from the recordcarrier to the magnetic head. Consequently, a long lifetime cannot beguaranteed for the known magnetic head whose head face also serves as atape contact face.

[0004] It is known per se to provide wear-resistant layers on the headfaces of magnetic heads in order to inhibit wear. EP-A 0 123 826(herewith incorporated by reference) proposes to provide the head faceof a magnetic head with a sputtered layer of titanium carbide, chromiumcarbide or titanium nitride which is thinner than 0.2 μm. However,magnetic heads whose head faces have a wear-resistant layer have theproblem that the transfer of information from the record carrier to themagnetic head is worse than in corresponding magnetic heads without awear-resistant layer on the head face. In order that more favourableoutput signals are still achieved during operation, it is required thatthe wear-resistant layer should not be made thicker than is strictlynecessary due to the wear-inhibiting function. Thin wear-resistantlayers, notably thinner than 100 nm, are generally not gas andmoist-proof so that corrosively reacting substances, notably from therecord carrier, can reach the head face via pores in the wear-resistantlayer. Notably soft-magnetic materials such as NiFe alloys are readilyaffected by corrosively reacting substances, resulting in a decrease ofthe transfer of information from the magnetic tape to the transducingelement. It has been found that many magnetic tapes contain, inter aliachlorine and that during scanning of these magnetic tapes Cl ionsdiffuse from the magnetic tapes into the head faces of the magneticheads where they cause local corrosion.

[0005] It is an object of the invention to improve the magnetic headdescribed in the opening paragraph in such a way that it has awear-resistant and corrosion-resistant head face.

[0006] The magnetic head according to the invention is characterized inthat the head face is provided with a first layer of a material which ismore sensitive to corrosion than said materials in the head face, andthe first layer is provided with a second layer of a wear-resistantmaterial which is more insensitive to corrosion than the material of thefirst layer.

[0007] The second layer, which constitutes a contact face forcooperation with a record carrier, protects the magnetic head accordingto the invention from abrasive and corrosive wear, while the first layerpresent between the head face and the second layer protects the magnetichead from corrosively reacting substances such as chlorine originatingfrom the record carrier. It has also been found that the adhesion ofwear-resistant materials to materials occurring in the head face can beimproved by suitable choice of the material of the first layer; in otherwords, the first layer may also serve as an adhesive layer.

[0008] To ensure a favourable signal transmission from the recordcarrier to the transducing element and/or from the transducing elementto the record carrier, said layers should have a minimal thickness.Favourable results were achieved with magnetic heads according to theinvention, whose first layer had a thickness of between 1 nm and 20 nmand whose second layer had a thickness of between 10 nm and 100 nm.However, a magnetic head is preferred whose first layer has a thicknessof less than 5 nm and whose second layer has a thickness of less than 60nm, because only very limited output losses occur in this case.

[0009] An embodiment of the magnetic head according to the invention ischaracterized in that the material of the first layer mainly comprises ametal from the group of—Ti, Zr, Hf, V, Nb, Ta, Cr, Al, Zn—. All thesenon-magnetic metals have lower standard reduction potential values, −E°values in accordance with the US definition—than Fe; thus, they are lessnoble than Fe so that soft-magnetic flux guides of, for example an NiFealloy—permalloy—terminating in the head face are protected fromcorrosion by the material of the first layer. The metals may be providedon the head face by means of known deposition methods, particularlyphysical or chemical vapour deposition such as sputtering or CVD.

[0010] An embodiment of the magnetic head according to the invention ischaracterized in that the material of the second layer is one of thematerials from the group of—chromium oxide, chromium nitride, hafniumnitride, titanium nitride, chromium carbide, titanium carbide, tungstencarbide, diamond—. All these materials have good wear-resistantproperties and adhere satisfactorily to the metals of the first layer.The materials may be provided on the first layer by means of knowntechniques such as sputtering deposition, vapour deposition or CVD. Forprocess-technical reasons the following combinations of materials arepreferred: titanium and titanium nitride or titanium carbide; hafniumand hafnium nitride; chromium and chromium oxide or chromium nitride orchromium carbide.

[0011] An embodiment of the magnetic head according to the invention ischaracterized in that the chromium oxide is mainly Cr₂O₃, the materialof the first layer being Cr.

[0012] This magnetic head according to the invention has awear-resistant contact face formed by the layer mainly comprising Cr₂O₃for cooperation with a record carrier, particularly a magnetic tape. Ata layer thickness of 10 nm to 100 nm a favourable signal transmissionbetween the record carrier and the transducing element is ensured. Ithas also been found that the contact face has a good wear resistance,not only in the temperature range between 5° C. and 85° C., but also attemperatures in the range between 5° C. and −20° C. This is particularlyimportant for magnetic heads which are used in portable apparatuses andin magnetic scanning devices intended for outdoor use, such as car radiocassette recorders.

[0013] It has been found by experiment that a qualitatively eminentlayer mainly comprising Cr₂O₃ on the head face can be obtained byproviding this layer by means of sputtering. Already at layerthicknesses of less than 60 nm, high wear resistances are found to beachievable by means of sputtering. A further advantage of the sputteredwear-resistant layer mainly comprising Cr₂O₃ is that it can be formed attemperatures of less than 300° C. The magnetic properties of magneticmaterials present in the layered head structure will then remainunaffected during formation of this layer. A wear-resistant layer mainlycomprising Cr₂O₃ and provided on the head face by means of sputteringyields a magnetic head according to the invention which suppliesfavourable output signals during operation and is suitable for use atrelatively low temperatures and, moreover, has a long lifetime.

[0014] It has been found by experiment that a layer having a thicknessof approximately 5 nm mainly comprising Cr and preferably provided bymeans of sputtering is sufficient to inhibit corrosion of the head faceand to ensure a satisfactory adhesion of the layer mainly comprisingCr₂O₃ to the head face.

[0015] The invention also relates to a method of manufacturing amagnetic head according to the invention, whose first layer mainlycomprises Cr and whose second layer mainly comprises Cr₂O₃. In thisconnection the invention has for its object to provide a method which isas simple as possible for manufacturing such a wear-resistant magnetichead.

[0016] The method according to the invention is characterized in that afirst layer mainly comprising Cr is formed on the head face, at least onthe head structure by means of sputtering deposition, and a second layermainly comprising Cr₂O₃ is formed on the first layer by means ofsputtering deposition.

[0017] An embodiment of the method according to the invention ischaracterized in that sputtering is performed with a chromium targetwithout oxygen addition until the first layer is formed, whereafteroxygen is supplied for forming the second layer. It has been found thatthe oxygen can already be supplied after the formed layer mainlycomprising Cr has a thickness of several nanometers. It has also beenfound that, provided it is not extremely low, the oxygen pressure has nosubstantial influence on the composition of the formed wear-resistantlayer mainly comprising Cr₂O₃, which renders the properties of thiswear-resistant layer independent of small process variations. Due to thereliability of the method, sputtering is only to take place in practiceuntil the formed layer mainly comprising Cr₂O₃ has a thickness ofapproximately 60 nm.

[0018] It is to be noted that it is known from IBM Technical DisclosureBulletin, vol. 11, no. 10, March 1969, pp. 1199 (herewith incorporatedby reference) to provide Cr₂O₃ by means of flame plating onheat-resistant magnetic heads for forming wear-resistant layers. JP-A66-73917 (herewith incorporated by reference) proposes to provide corelimbs of permalloy comprising Cr with a layer of Cr oxide having athickness of more than 0.5 μm and to form a layer of Cr oxide by meansof sputtering on core limbs of permalloy not comprising Cr.

[0019] These and other aspects of the invention will be apparent fromand elucidated with reference to the embodiments described hereinafter.

[0020] In the drawings

[0021]FIG. 1 is a layout of a first embodiment of the magnetic headaccording to the invention,

[0022]FIG. 2 is a diagrammatic cross-section taken on the line II-IIthrough a transducing gap of the magnetic head of FIG. 1,

[0023]FIG. 3 is a perspective elevational view of the magnetic head ofFIG. 1, and

[0024]FIG. 4 is a perspective elevational view of the magnetic head ofFIG. 1 in a production stage in which the magnetic head still has anuncoated head face.

[0025] The thin-film magnetic head according to the invention shown inFIGS. 1, 2 and 3 comprises a support or substrate 1, in this example ofa magnetic material, viz. NiZn ferrite on which a head structure 2composed of magnetic layers, electric layers and insulating layers isprovided. The head structure 2 composed by means of thin-film techniquesis protected by a counterblock 3 of a non-magnetic material, for exampleAl₂O₃/TiC. The magnetic head has a head face 5 with eleven transducinggaps in this example. A group of nine gaps S1 to S9 of the eleventransducing gaps is intended for reading information in a digital formand one pair of gaps S10 and S11 is intended for reading information inan analog form on a record carrier 7 which moves along the magnetic headin a direction x. The gaps S1 to S9 for digital use generally have asmaller gap length than the gaps S10 and S11 for analog use. Moreover,the gap length may be chosen to be such that both analog and digitalinformation can be read by one and the same gap.

[0026] The magnetic head according to the invention comprises aninsulation layer 9 provided on the substrate 1, which insulation layeris provided with three electric conductors C1, C2 and C3 in thisexample, which conductors may extend into the transducing gaps. Themagnetic head also comprises eleven magnetoresistive elements E1 to E11,further referred to as MR elements which comprise, for example a layerof NiFe on which one or more equipotential strips, for example of Au maybe provided. The MR elements E1 to E11 are each provided with a pair offirst connection tracks 11 a and 11 b which terminate in firstconnection faces 13 a and 13 b, respectively. Both the first connectiontracks and the first connection faces are preferably made of Au. It isto be noted that an MR element provided with equipotential strips isknown per se and is described inter alia in U.S. Pat. No. 4,052,748(herewith incorporated by reference).

[0027] Said electric conductors C1, C2 and C3 are used for biasing theMR elements E1 to E9, E10 and E11 and are each provided with a pair ofsecond connection tracks 15 a and 15 b which terminate in secondconnection faces 17 a and 17 b, respectively.

[0028] The magnetic head also comprises eleven pairs of flux guides of asoft-magnetic material, for example permalloy, each pair comprising afirst or front flux guide 19 a and, spaced apart therefrom, a second orrear flux guide 19 b. The front flux guide 19 a extends as far as thehead face 5 for cooperation with the magnetic record carrier 7. The MRelements E1 to E11 are present between the substrate 1 and the fluxguides, each MR element constituting a bridge between a first and asecond flux guide 19 a and 19 b. In certain constructions and forcertain uses it is possible to omit the rear flux guides. It is alsopossible to start from a non-magnetic substrate and to provide an extraflux guide.

[0029] The electric conductors, the MR elements and the flux guides areelectrically insulated from each other by a plurality of insulationlayers of an electrically and magnetically insulating material, forexample an oxide or a polymer. The insulation layers are denoted by thereference numerals 21 and 23 in FIG. 2. A further insulation layer 25 inthe form of, for example an adhesive layer is present between the sharedflux guides 19 a and 19 b and the counterblock 3.

[0030] A first layer 31 mainly comprising Cr is provided on the headface 5 of the magnetic head according to the invention, while a secondlayer 33 mainly comprising Cr₂O₃ is provided on the first layer forforming a wear-resistant contact face 35 for cooperation with thetape-shaped record carrier 7. On the one hand, the first layer 31ensures a satisfactory adhesion of the second layer to the magnetic headand on the other hand protects the materials of the head structure,particularly the soft-magnetic materials from attack by exterioraggressive substances.

[0031] The method of providing the layers 31 and 33 on the head facewill now be described with reference to FIG. 4. After the assembly ofsubstrate 1, head structure 2 and counterblock 3 has been provided withthe contact face 5, for example by means of grinding and/or polishing,the assembly is placed in a known sputtering device comprising achromium target. By means of reactive RF sputtering, for example RFdiode sputtering at 10 mTorr Ar, mainly Cr is deposited on the head face5 at the transducing gaps S1-S11 and at both sides thereof.

[0032] After a given layer thickness, for example 5 nm has been formedby deposition of Cr, oxygen is supplied to the sputtering device, whilethe layer mainly comprising Cr₂O₃ is formed at, for example 1 mTorr. Anadvantage of this method is that the two layers can be provided rightafter each other, using the same sputtering device.

[0033] It is to be noted that the invention is not limited to theembodiment shown. For example, the magnetic head according to theinvention may comprise one or more inductive transducing elementsinstead of or in addition to magnetoresistive transducing elements forrecording information on a record carrier. Moreover, instead of awear-resistant layer of Cr₂O₃, a layer of a different material from thegroup of chromium oxide, chromium nitride, hafnium nitride, titaniumnitride, chromium carbide, titanium carbide, tungsten carbide anddiamond may be used as a wear-resistant layer. Instead of Cr, a metalfrom the group of Ti, Zr, Hf, V, Nb, Ta, Al and Zn may be used forforming an intermediate layer extending between the head face and thewear-resistant layer.

1. A magnetic head having a head face and comprising a head structurecomposed of thin layers and provided with a transducing element, inwhich different materials in different areas are present in the headface, characterized in that the head face is provided with a first layerof a material which is more sensitive to corrosion than said materialsin the head face, and the first layer is provided with a second layer ofa wear-resistant material which is more insensitive to corrosion thanthe material of the first layer.
 2. A magnetic head as claimed in claim1, characterized in that the first layer has a thickness of between 1 nmand 20 nm and the second layer has a thickness of between 10 nm and 100nm.
 3. A magnetic head as claimed in claim 1 or 2, characterized in thatthe material of the first layer mainly comprises a metal from the groupof —Ti, Zr, Hf, V, Nb, Ta, Cr, Al, Zn—.
 4. A magnetic head as claimed inclaim 1, 2 or 3, characterized in that the material of the second layeris one of the materials from the group of—chromium oxide, chromiumnitride, hafnium nitride, titanium nitride, chromium carbide, titaniumcarbide, tungsten carbide, diamond—.
 5. A magnetic head as claimed inclaim 3, characterized in that the chromium oxide is mainly Cr₂O₃, thematerial of the first layer being Cr.
 6. A method of manufacturing amagnetic head as claimed in claim 5, characterized in that a first layermainly comprising Cr is formed on the head face, at least on the headstructure by means of sputtering deposition, and a second layer mainlycomprising Cr₂O₃ is formed on the first layer by means of sputteringdeposition.
 7. A method as claimed in claim 6, characterized in thatsputtering is performed with a chromium target without oxygen additionuntil the first layer is formed, whereafter oxygen is supplied forforming the second layer.